Many communication devices operate on battery power. For the convenience of the user, communication devices may be designed for use with commonly available batteries, such as "AA" or "AAA" cells. Two such cells in series provides an approximately 3.0 volt DC battery voltage. The communication device includes a DC-to-DC voltage converter to step up the battery voltage to an operating voltage, such as 5.0 volts. The voltage converter thus provides the operating voltage for the communication device.
Such voltage converters are not one hundred percent efficient, however. One commonly available voltage converter is approximately 80% efficient over an output current range of several hundred milliamps (mA). Efficiency is the ratio of the output power to the input power for the voltage converter. For output currents above about 600 mA, converter efficiency falls off rapidly. These values are representative only. Other voltage converters will have other efficiencies and other operational limitations.
The effect of reduced voltage converter efficiency at high current is increased power drain from the battery. As output current from the voltage converter increases, current drain from the battery increases proportionate to efficiency. If efficiency decreases as the output current increases, the current drawn from the battery will increase proportionately with both increasing output current and decreasing efficiency. Thus, at high current, the battery discharge rapidly, inconveniencing for the user.
Communication devices can be designed with low power dissipation to keep the current drawn from the voltage converter in a range of greatest efficiency. However, as portions of the communication device switch on and off, peak current drawn from the voltage converter may temporarily move the voltage converter into a low efficiency range. If such peaks occur frequently or are sustained in duration, the batteries will discharge rapidly.
Accordingly, there is a need for a method and apparatus for reducing the magnitude and duration of current peaks drawn from a voltage converter in a communication device.